Proportion of the Precept to Subject Matter with an Approach to the Custom's Instrumental Function

Prior to deducing Islamic precepts, a jurist's mission is to know the effective method of ijtihad without which gaining access to the Shariah is impossible. In Shariah, the religious precepts are categorized in three main categories of precepts, precept's subject matter, and the dependent. Occasionally, in deducing religious precepts, subject matter is liable to some changes depending on the subject, circumstances, or some conditions which end in the change of the precepts to be issued. Congruence of precept and subject matter include cases and criteria that while referring to a reason, it attracts one's attention to itself unconsciously. The present paper has attempted to illustrate the existing relations between the subject matter and the precept and its significance from outstanding Shia jurisprudent's and Osuli scholar's perspectives. The author believes that by the virtue of authentic texts (nosus) and traditions (ahadith), one might issue a primary precept irrespective of trapping in analogy and he does not need to resort to secondary subject so much.